Variable reactive microwave device



Nov. 28,1950 J. EVANS VRIABLE REACTIVE MICROWAVE DEVICE Filed oct. 31, 1944 l IN1/Emme.` QUL Evang N f www@ T, @www s Patented Nov. 28, 1950 VARIABLE REACTIVE MICROWAVE DEVICE John Evans, Kingston, N. E., assignor to Radio `Corporation of America, a corporation of Dela- Ware Application Dctober 31, 1944, Serial No. 561,277

This invention relates generally to microwave transmission systems and more particularly to an` improved method of and means `for adjusting reactance or attenuation in a microwave communication system. A

It has been found' that the effective dielectric constant of certain gases, liquids and solids varies as a function of the electric or magnetic field to which the dielectric is subjected. This eiect is bel-ievedwto be causedby the` orientation of: molecular or crystal-linedipolesof' the particu-lar material in` planes which are parallel to the directionof the applied iield; In dielectrics wherein the molecular dipoles are ofsubstantially insulating material, the orientation of- `the molecular diploes may be producedbyv means of an applied el'ectrostatic eld. In materials which include comminuted or molecular conducting particles, such,for examplaas `comminuted iron, the orientation of the particles may be produced by means of an appliedwmagneti-c field.

Inthe absence of an applied held, the molecular dipoles ofy the dielectric material have random orientation; However, inthe `presence ofa biasing field, the orientati-onr `of the molecular dipoles in planes parallel to the i'leld produces: a secondary field which will oppose the propagation of microwaves through "the dielectric-material Hence, a dielectric of any or the types described may be enclosedN within a conventional waveguide transmission system to. provide a waveguide section having reactance; phaser rotation, oratt'enuation which varyr as a function of an applied biasing electrostaticY or magnetic field', depending upon the dielectric material employed.

Avariable reactivewaveguide` section of the type described` may be `employed' for controlling the phase, amplitude `or frequency of microwaves transmitted `through an otherwise `conventional waveguide system-f.

Among the objects of the invention are toA provide an improvedmethod of and' means for-varying` reactance in` a waveguide transmission system Another object of the invention is to provide: an improved method `of and means for adjusting attenuation in- `a waveguide transmission system. A further objectoi" the invention is te providef an improvedmethod of and means` :for phase modulating microwave energy. Anadditional object iste provide anf improved method of andl means for amplitude modulating microwave energy. Another object of the `invention is to provide an improved method of and `means for frequency modulatingmicrowave` energy.

A still further object"` ofthe `invention is `to 12` Claims. (CL. 17g-44) provide an improved method of and means for adjusting the dielectric constant of a dielectric enclosed within a section of a waveguidetransmission system.` Another objectof the invention is to provide an improved microwave variable reactance comprising a section of waveguide enclosing a material oi4 which the dielectric constant maybe varied as a function of an applied field. Other objects of the invention will become apparent in View ofthe more: detailed description which follows, considered in combination with the appended claims.

The invention will be described in greater detail by reference to` the accompanying drawing oit? which Figure `1 isr a perspective view of one embodiment of the invention; Figure 2 is an elevational `cross-sectional view, taken along the section line Ill-II, of the device `illustrated in Figure 1; Figure 3 is a cross-sectional elevational viewbf an optional `cross-sectional structure for the device illustrated in Figure l;` Figure 4 is a schematic circuit diagram of one system embcdiment of the invention; Figure 5 is a schematic circuit diagram `of a second system embodiment `ofA the invention; and Figure 6 is a schematic circuit diagram of a third system embodiment of ,the invention. Similar reference characters are applied to similar elements throughout the drawing.

Referring to Figures 1 and 2 of the drawing, a preferred embodiment of the invention comprises a pair of U-shaped insulating channel members 3, 5; of polystyrene or other insulating material, joined together on the lines T, 9, to provide a waveguide of rectangular cross-section. The inner surfaces of the insulating dielectric channels 3, 5 are coated with conductive layers Il, i3 eX- cept in the immediate vicinity of the joints l', 9. A conductive coating may be `applied tothe polystyrene walls by employing an ethylene dichloride and styrol cement in combination with powdered silver `to provide a continuous silver coating havingl high electrical conductivity. Since the conductivelayers `l I, `I3. on theinsulating waveguide walls 3, 5 are" insulated from each other by the gaps adjacent the joints l, t, the opposing conductive elementsmay be employed for establishing a dielectric field in a vertical plane within the waveguide. Contacts l i5, l1; extending through the dielectric waveguide walls 3, 5 respectively, and electrically connected to the conductive layers H', l3, respectively, may beconnected, for example, through a biasing battery t8 to the secondary winding |19 of a pulse transformer 2li, to the primary winding 23. ot which` may be applied keying pulses or other modulation signals from a source not shown. If the use of a modulation transformer is not practicable, the modulation signals may be applied directly or through any other known means to the contacts I5, Il.

Polystyrene windows Z5, 2'1 extending across the entire inner cross-section of the waveguide section adjacent the ends thereof, provide a sealed chamber 39 in which a predetermined gas, liquid, or solid dielectric material having a variable dielectric constant may be enclosed. The length of the enclosed chamber within the waveguide section may be selected to be of the order of 1/4 or 1X2 wavelength as desired. However, the length of the adjustably reactive chamber may 'oe otherwise selected to conform with the reactive requirements oi the particular associated microwave circuit. In order to minimize microwave reflections due to the discontinuities provided by the polystyrene windows 25, 27, one or more reactive tuning plugs 29, 3i may be provided in the connecting waveguide adjacent each end of the variably reactive waveguide section. Both ends of the variably reactive waveguide section may include conductive flanges 33, for connection to adjacent conventional rectangular waveguides as, for example, the waveguide 3l' including the tuning plugs 29 and 3l.

The enclosed chamber 39 between the polystyrene windows 25, 2l may be lled either with a gaseous, liquid or solid dielectric in which the dielectric constant varies with the strength of an applied field. A typical liquid having these characteristics comprises nitrobenzol having quinine crystals emulsied therewith. Under the stress of an applied electrostatic eld, the quinine crystals are oriented in planes parallel to the applied eld. Various other materials may be employed either singly or in combination with neutral supporting liquids such as nitrobenzol.

A typical solid in which the molecular dipoles may be oriented by the application of a dielectric i'leld is titanium dioxide (T102). In the case of both the liquids and the solids enumerated heretofore, the dielectric eld may be modulated directly by means of the modulating potentials to provide a section of waveguide having variable reactive or attenuating characteristics to microwaves propagated therethrough. It should be understood that the variations in dielectric constant, in the liquid or solid mediums employed, provides a corresponding variation in the propagation velocity of microwaves transmitted therethrough.

Certain gases such, for example, as ammonia, also may be employed as variable microwave absorptive dielectric materials since these gases absorb microwave energy within predetermined frequency ranges. For example, ammonia gas absorbs microwave energy at wavelengths in the region of 3.2 centimeters and 1.1 centimeter. Thus, the modulation applied to the control cell terminals i5, l1 may comprise 3.2 centimeter wavelength which are modulated by means of the desired low frequency keying or modulating signals. The variable dielectric constant or loss characteristics of the gas due to phase rotation thence may be employed to modulate microwaves having a wavelength, for example, of the order of two centimeters which are propagated through the waveguide system. Thus, it is seen that the variable dielectric constant or loss characteristics of various gases, liquids, or solids may be modied in accordance with the modulating potentials to vary the reactance, or attenuation, of a waveguide section forming a control cell portion of a microwave waveguide system. Insofar as liquid dielectrics are concerned, the speed of response to applied modulation signals is a function of the viscosity of the liquid. This eiect has not been fully investigated with gases or solid dielectrics.

Figure 2 illustrates schematically the parallel orientation of the molecular dipoles 4l of an insulating material in response to an applied electrostatic field established between the conductive waveguide surfaces H, I3.

Figure 3 illustrates a modification of the device described in Figures 1 and 2 wherein the waveguide section includes conventional conductive wallsli closed at each end by a polystyrene window as illustrated at 25. A portion of the window 25 is shown broken away to illustrate the use of a magnetically sensitive dielectric 45 within the space between the dielectric windows 25, 2l. A pair of magnetic pole pieces 41, 49, including serially-connected windings 5I, 53, respectively, connected to the secondary winding it of the modulation transformer 2|, provide a magnetic held transversely of the waveguide section which may be employed to vary the dielectric constant of the enclosed material 45.

A. dielectric in which the dielectric constant may be varied in response to an applied magnetic eld may, for example, comprise nitrobenzol having finely comminuted iron dust in emulsion therewith. Application of a transverse magnetic field between the pole pieces 41, 49 causes the comminuted iron particles to arrange themselves in planes parallel to the magnetic eld, thereby changing the eiective dielectric constant of the emulsion in the same manner as described heretofore for the embodiment of the invention employing a modulating dielectric field. It should be understood that the use of nitrobenzol as a support for the comminuted iron particles is purely illustrative, and that various other neutral supporting liquids may be employed in a similar manner.

Also, it should be understood that other magnetic materials, such as comminuted nickel, may be substituted for the comminuted iron in the magnetically sensitive emulsion. The modication of the invention illustrated in Figure 3 has the advantage that a conventional section of waveguide, having continuous metallic walls, may be employed for the variable reactance control cell device.

Since the reactance or attenuation of the devices thus described may be varied within wide limits, they are ideally adapted to provide modulating elements for conventional microwave transmission systems. For example, as illustrated in Figure 4, the control cell comprising the invention may be interposed between a microwave receiver and a microwave antenna in a waveguide coupling system wherein a microwave transmitter is connected through an auxiliary waveguide to the same microwave antenna. A transmitter 6| is connected through a waveguide 63 to a microwave antenna. Similarly,` a microwave receiver 55 is connected through a receiver waveguide 5l to the same antenna as, for example, in radar systems. The control cell 69 may be interposed in the receiver waveguide 5l' at a point, for example, 1/4 wavelength from the junction with the transmitter waveguide 63. The source of keying pulses 'H which keys the accenna transmitter 6+; a'sindicatedby thee' dash line 13. also maybeiconncctedtofthe control cell` 69 to block signals in the receiver wavegudef'l* when the transmitter 6I is keyedion. Thekeying pulses from the keying pulse source 1|" thus may provide an effective short circuit across the control ceill 69 when the Ytr-ansmitteni'skeyed on, thereby' providing arelatively"` highl impedance looking into* thereceiver waveguide BJ at `the point where it `joins the transmitter waveguide163l. In the absence ofrtransmitter key-ing pulses, the control cellL eiliciently` transmits` to the receiver the-signalsderived from therantenna.

Figure` 5 i illustrates schematically the manner in-whichthe control cell- 69'1maybe seriallyfinterposed -in a waveguide transmission system 63 connecting a microwave transmitter Slitoaload 15. Since the control cell provides variable delay of microwave signals applied therethrough to the load 'l5 due to the variations in microwave propagation velocity, the modulation voltage source H may be connected to the control cell to vary the phase of signals applied to the load 15. The effective length of the control cell and/or the magnitude of the modulating signals may be selected to provide the desired phase shift in response to modulation potentials.

Figure 6 schematically illustrates the manner in which the control cell 69 may be employed for frequency-modulating a source of microwave oscillations. In this modication of the invention, the control cell may comprise, for example, all or a portion of a cavity resonator forming the tank circuit of the oscillation source. The effective reactance of the control cell 69 may be varied by means of the modulation voltage source 'Il' in the same manner as described heretofore, thereby providing corresponding variations in the frequency of the microwave oscillations generated by the oscillator tube Tl. The output of the oscillator 'Vl is applied directly, or through suitable coupling circuits, to the load 15. It should be understood that the structure and conformation of the control cell may be varied in any manner known in the microwave art to provide the desired type of oscillator tube tank circuit. The rectangular waveguide structure described and specically illustrated herein is intended purely for the purpose of illustration, since the control electrostatic or electromagnetic fields may be applied to an enclosed eld-responsive dielectric in any other structure o1' manner known in the art.

Thus the invention described comprises an improved method of and means for varying reactance or attenuation in a microwave transmission system wherein predetermined dielectrics, having dielectric constants dependent upon an applied eld, are employed to provide variable reactance, delay, or loss chracteristics in a waveguide transmission system.

I claim as my invention:

l. In combination with a waveguide transmission system, a variable reactive device comprising a section of waveguide containing a pliant dielectric, particles of solid material mixed with said dielectric, means for establishing a iield transversely of said waveguide section for orienting said particles, and means for selectively varying said field to vary the reactive properties of said device.

2- In combination with a waveguide transmission system, a variable reactive device comprising a section of waveguide containing a liquid dielectric, comminuted particles of solid mate- 6? riai formingranfemulsion with:said-liquidl dielectric, means for establishingfa: field transversely ofi said;l waveguidefsection fororienting said i particles, an'dfmeans for selectively varyingfsaid ii'eld to vary-A the reactive, properties-of saidl device,

3. In combinationwitha waveguide transmission' system, a variablereactivefdevice comprising a; secti'omoffwaveguide'- containing a pliant dielectric, `comminuted-lparticles of solid1 magnetic. material forming anlemulsion` with said dieiectric'; means` for establishing a magnetic eld transversely ot `said waveguide" section for orienting saidtparticles; and meansV for l selectively varying said ieldf to `vary-the reactive properties offsaiddevice.

4'. In combi'nation4 with aL waveguide transmission system, a variable reactive-device-- comprisingia'- section ofrwaveguide con-taininga pliant dielectric, comminuted particles of solidl dielectric materialforming an emulsion with said pliant dielectric, means for establishing an electric eld transversely of said waveguide section for orienting said particles, and means for selectively varying said eld to vary the reactive properties of said device.

5. In combination with a waveguide transmission system, a variable reacting device comprising a section of waveguide having insulating walls and containing a liquid dielectric, crystalline particles of solid dielectric material forming an emulsion with said liquid dielectric, means including relatively insulated conductive inner surfaces of said insulating waveguide walls for establishing an electric eld transversely of said waveguide section for orienting said particles, and means for selectively varying said iield to vary the reactive properties of said device.

6. In combination with a waveguide transmission system, a variable reactive device comprising a section of waveguide containing a liquid dielectric, comminuted particles of solid magnetic material mixed with said liquid dielectric, means including a magnetic structure having pole pieces disposed adjacent opposite sides of said waveguide section for establishing a magnetic field transversely of said waveguide section for orienting said particles, and means for selectively varysaid field to vary the reactive properties of said device.

7. A variable reactive device comprising a section of waveguide containing a pliant dielectric, particles or solid material mixed with said dielectric, and means for establishing a eld transversely of said waveguide for orienting said particles to vary the reactance of said device.

8. A variable reactive device comprising a section of waveguide containing a liquid dielectric, comminuted particles of solid material mixed with said liquid dielectric, and means for establishing a eld transversely of said waveguide for orienting said particles to vary the reactance of said device.

9. A variable reactive device comprising a section of waveguide containing a pliant dielectric, comminuted particles of solid magnetic material mixed with said dielectric, and means for establiehing a magnetic eld transversely of said waveguide for orienting said particles to vary the reactance of said device.

10. A variable reactive device comprising a section of waveguide containing a liquid dielectric, crystalline particles of solid dielectric material mixed with said liquid dielectric, and means for establishing an electric eld transversely of said waveguide for orienting said particles to vary the reactance of said device.

l1. vA variable reactive device including asection of waveguide containing nitrobenzol comprising a liquid dielectric, crystalline particles oi 5 quinine mixed with said liquid dielectric, and means for establishing an electric eld transversely of said waveguide for orienting said particles to vary the reactance of said device.

12. In combination with a waveguide transmission system, a variable reactive device comprising a section of waveguide containing a pliant dielectric including particles of solid material of the group including solid dielectric material, magnetic material, and crystalline guinine, means for establishing a eld transversely of said waveguide section for orienting said particles, and means Yfor selectively varying said field to vary the reactive properties of said device.

v JOHN EVANS.

REFERENCES CITED The following references are of record in the le of this patent:

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